Early prediction of response to intravenous iron supplementation by reticulocyte haemoglobin content and high-fluorescence reticulocyte count in haemodialysis patients

BACKGROUND

Optimal response to recombinant human erythropoietin (rHuEpo) in haemodialysis (HD) patients requires provision of sufficient available iron. However, a balance between iron requirements and supplements remains a challenge in clinical practice. Reticulocyte parameters, i.e. reticulocyte haemoglobin content (CHr) and reticulocytes in a high-fluorescence intensity region (HFR), have been shown to be accurate predictors of iron-deficient erythropoiesis as compared with traditional markers. Therefore, the aim of this study was to appraise the diagnostic power of these two parameters in the early prediction of response to intravenous iron (IVFE) medications in HD patients receiving rHuEpo.

METHODS

Sixty-five HD patients with a serum ferritin level of <500 microg/l and on rHuEpo therapy for >6 months were enrolled for IVFE supplementation (100 mg iron saccharate three times a week for 4 weeks, then 100 mg every 2 weeks for 5 months). Haemoglobin, haematocrit, serum ferritin, transferrin saturation, reticulocyte count, percentage of hypochromic red cells, CHr and HFR were measured before and following iron supplementation. Response was defined as a rise in haematocrit of >3% and/or a reduction in rHuEpo dose of >30% over the baseline values at the end of the study.

RESULTS

Forty-two patients had a dramatic response to IVFE therapy with a 13.5% increase in mean haematocrit and a 38% reduction in rHuEpo dose at the end of the study (P<0.001). This paralleled a statistically significant rise in CHr and HFR (P<0.001). Univariate analyses showed that ferritin (P<0.010) and CHr (P<0.001) at baseline, changes in CHr (DeltaCHr(2W), P<0.001) and HFR (DeltaHFR(2W), P<0.010) at 2 weeks, as well as changes in CHr (DeltaCHr(4W), P<0.001) and HFR (DeltaHFR(4W), P<0.001) at 4 weeks, strongly correlated with response to IVFE supplementation. Stepwise discriminant analysis disclosed that DeltaCHr(4W) in conjunction with DeltaHFR(4W) exhibited an r(2) value of 0.531 (P<0.001) to predict response to IVFE therapy. Analyses by receiver operating characteristic curves and logistic regression further revealed that DeltaCHr(4W) at a cut-off value of >1.2 pg and DeltaHFR(4W) of >500/microl were more specific to the status of iron-deficient erythropoiesis following IVFE medications. Combined use of the two cut-off values allowed for the highest accuracy in the early prediction of the response to IVFE therapy, with a sensitivity of 96% and a specificity of 100%.

CONCLUSIONS

Our study shows that changes in CHr and HFR at either 2 or 4 weeks are superior to the conventional erythrocyte and iron metabolism indices and may serve as reliable parameters to detect iron-deficient erythropoiesis in HD patients undergoing rHuEpo therapy. During aggressive IVFE treatment, early identification of non-responsiveness and subsequent discontinuation of treatment can avoid the inadvertent iron-related toxicity due to over-treatment.

Effects of phenylhydrazine or recombinant human erythropoietin on deformability and activity of dehydrogenase glucose-6-phosphate and acetylcholinesterase in Wistar rats blood enriched in reticulocytes

Deformability and activity of the enzymes: acetylcholinesterase (AChE) and dehydrogenase glucose-6-phosphate (G-6-PD), were assayed for RBC enriched in immature reticulocytes. Reticulocytosis was evoked by administration of two different drugs: recombinant human erythropoietin (rHuEPO) and phenylhydrazine (PHZ) to two groups of Wistar rats. After treatment with the former compound, a group of animals exhibited 17.33% reticulocytes in blood whereas a group of rats treated with the latter drug reached 57.66% of these cells in blood. A marked decrease in RBC deformability was found in both groups of animals. AChE did not significantly change activity neither in PHZ-treated nor in rHuEPO-treated rats, whereas G-6-PD activity was significantly decreased in the PHZ-treated group.

Five fully automated methods for performing immature reticulocyte fraction: comparison in diagnosis of bone marrow aplasia

We performed a parallel evaluation of 5 automated reticulocyte counters to produce the immature reticulocyte fraction (IRF). We analyzed 225 samples from healthy control subjects, 115 from patients with various diseases, 38 with advanced aplasia, and 22 in early erythropoietic recovery after chemotherapy or bone marrow transplantation. The reference intervals were different for each instrument (ADVIA 120, 0.04-0.25; CELL DYN 4000, 0.15-0.35; GEN-S, 0.20-0.37; SE 9500 RET 0.05-0.21; VEGA RETIC: 0.06-0.23). The imprecision, obtained by 1-way analysis of variance on duplicates, was satisfactory for clinical use for all methods (coefficient of variation, 7.6%-20.5% in healthy subjects), although it was higher than the analytic goal based on biologic variability within subjects. The comparison of different methods shows that agreement is good only between SE 9500 RET CELL DYN 4000, and VEGA RETIC (r2 = 0.72-0.78). The study of diagnostic performance in distinguishing aplasia from early bone marrow recovery shows slightly different results (area under the curve from 0.70 for ADVIA 120 to 0.96 for SE 9500 RET). Even with slight differences, the fluorescence-based methods seem to be more robust than other methods for IRF measurement.

Changes in erythropoiesis assessed by reticulocyte parameters during ultralong distance running

OBJECTIVE

To investigate the possibility of early changes in erythropoiesis during prolonged exercise being reflected in reticulocyte parameters.

DESIGN

This was a case-control field study of hematological variables in a group of ultramarathon runners competing in a 6-day track race.

SETTING

A 6-day ultramarathon in Colac, Australia.

PARTICIPANTS

7 male and 1 female experienced ultramarathon runners.

INTERVENTION

A track race of 6 days' duration.

MAIN OUTCOME MEASURES

A wide range of red cell and reticulocyte parameters.

RESULTS

Resting red cell parameters were within normal clinical limits. However, except for the expected findings typical of hemodilution, red cell parameters were relatively unchanged during and after the event, with the exception of small but statistically significant changes in number and percentage of macrocytic, microcytic, hypochromic, and hyperchromic red cells. No reticulocytosis was found in an event that would have been expected to be associated with significant foot-strike hemolysis; however, an increase in the percentage of reticulocytes with high RNA content late in the event indicates early release from the marrow. Reduction in reticulocyte mean cell volume, which is consistent with functional iron deficiency, was demonstrated during the event. This finding is consistent with changes in some of the iron-related parameters associated with the acute phase response, but the dissociation in time between these changes makes a causal relationship unlikely. Other changes such as those in reticulocyte hemoglobin distribution width, reticulocyte distribution width, cell hemoglobin concentration mean, and lack of change in corpuscular hemoglobin are not typical of true iron deficiency, and the mechanism of these changes is currently unknown.

CONCLUSION

The hematopoietic system demonstrates remarkable stability in the face of very significant exercise stress. No reticulocyte response was demonstrated in this study, but reticulocyte changes both consistent with and contrary to early release from the marrow were demonstrated after several days of strenuous running. The significance of several newly developed ratios of red cell and reticulocyte parameters in conditions of exercise stress requires further investigation.

Autophagy in hepatocytes and erythropoietic cells isolated from the twenty-one day old rat embryo

Liver cells of the twenty-one day old rat embryo are isolated by a modified method and autophagy is studied in them by electron microscopic morphology and morphometry. Immediately after isolation or 2.5 h incubation in nutrient-free medium, embryonic hepatocytes contain high amount of glycogen and only very few autophagic vacuoles. In contrast, all glycogen is lost and 15% of the cytoplasmic volume is occupied by late autophagic vacuoles in hepatocytes after 18 h in the same medium. Presence of 3-methyladenine in the latter case inhibits both the loss of glycogen and the appearance of autophagic vacuoles while enlarging the multivesicular body compartment. Our findings reveal major differences between isolated embryonic and adult hepatocytes concerning autophagy. Several types of autophagic vacuoles are described in the cell types of the erythropoietic cell lineage. This means that autophagy is an integral part of erythropoiesis not only in bone marrow, but also in embryonic liver that is investigated here for the first time from this point of view. The presence of unclosed isolation membranes and the predominance of early autophagic vacuoles in reticulocytes indicates that the molecular machinery of segregation is still active in this functionally and structurally highly reduced cell type.

Reticulocyte analysis by flow cytometry and other techniques

Enumeration of peripheral blood reticulocytes is an essential part of the diagnosis and management of anemic patients, since the number of reticulocytes in the peripheral blood reflects the erythrocytic activity of the bone marrow. Reticulocyte enumeration using flow cytometric methodology is rapidly replacing the inaccurate, imprecise manual counting technique used in the past. This article explores the pathophysiology of the reticulocyte, the various means of counting reticulocytes, and the diverse clinical applications of reticulocyte data.

[Treatment of anemia in rheumatoid arthritis with transplantation of hemopoietic stem cells from human embryonic liver]

The article describes chief links of pathogenesis of anemia in rheumatoid arthritis (RA). These include the blood hyperviscosity syndrome, abnormalities of iron metabolism, blockade of iron in the reticuloendothelial system, hemolysis, depression of erythropoiesis. Indices for the hemoglobin peripheral blood, erythrocytes, reticulocytes, platelets in the group of RA patients were analysed together with their changes under exposure to transplantation of hemopoitic stem cells of human embryional liver.

Carnitine action on red blood cell osmotic resistance in hemodialysis patients

Low red blood cell osmotic resistance (RBCOR) in dialysis patients aggravates anemia and raises EPO needs. We studied RBCOR in 30 stable patients (22 M, 8 F), dialyzed for more than one year, with no systemic illness, blood transfusions, recent infection or treatment by ACE inhibitors. Nineteen were on EPO. Cuprophane dialysis membranes were used in 21, synthetic in the remaining nine. RBCOR was low in 13 patients and these patients received L-carnitine, 20 mg/kg IV, post dialysis, for one year (A); 17 with normal RBCOR served as untreated controls (B). We investigated the relations between RBCOR and membrane material, time on HD (THD), weekly dialysis duration (WHDT), serum total carnitine (TC), acyl carnitine (AC), free carnitine (FC) and AC/FC in all patients, before and after carnitine supplementation. RBCOR changes under carnitine treatment were evaluated. Age, sex, primary renal disease, THD, EPO dose, hematology and biochemistry were similar in treated patients and controls. Patients in group A (dialysed with cuprophane) had lower RBCOR than group B, (dialysed with synthetic and cuprophane membranes) (0.473 +/- 0.02 vs. 0.420 +/- 0.02, P < 0.001). RBCOR remained stable under carnitine in group A, but became abnormally low in controls (especially in 10/17 patients). RBCOR was significantly higher than the pretreatment values in 5/13 group A patients (month 0-M0: 0.48 +/- 0.02, M12: 0.45, +/- 0.02, P < 0.05). Carnitine levels, similar in both groups before treatment, remained stable in group A, but dropped in group B (TC: 52.1 +/- 9.6/31.1 +/- 21.2, FC: 33.1 +/- 8.3/15.6 +/- 19.2 micromol/L, P < 0.002). Patients with shorter WHDT (< or = 12 vs. > 12 h) had higher FC levels (36 +/- 6.9 vs. 30 +/- 6 micromol/L, P < 0.03). Low RBCOR is frequent in stable dialyzed patients. It is related to dialysis membranes and is aggravated by time on hemodialysis. Serum carnitine levels depend on weekly dialysis time and on carnitine supplementation, that normalizes osmotic resistance in some dialysis patients.

[Autoimmune hemolytic anemia]

Autoimmune hemolytic anemia (AIHA) is subclassified according to the character of the autoantibodies, however, its clinical pictures are highly heterogenous even in a given subclass. In this article, we reviewed pathogenesis, clinical and laboratory characteristics of AIHA, exemplifying data of 26 patients with autoimmune hemolysis with warm-type autoantibodies (13 AIHA, 10 Evans' syndrome, 3 systemic lupus erythematosus), and recent advances in this field. White blood cell and platelet counts varied among patients at presentation. Six of 13 AIHA patients had low reticulocyte production index (RPI) indicative of inappropriate reticulocyte response with considerable erythroblasts in the bone marrow, suggesting that ineffective erythropoiesis contributes the pathogenesis of warm-type AIHA. Ten patients were judged to require red cell transfusion. Their RPI did not differ from that of patients who did not require transfusion, indicating that the degree of hemolysis is the major determinant of the severity of the disease. No significant side effects of transfusion were observed.

Role of reticulocytes on gametocytogenesis in chickens infected with Leucocytozoon caulleryi

Reticulocytes, known as late polychromatic erythrocytes, were induced in blood of chickens infected with Leucocytozoon caulleryi by bleeding when the second-generation merozoites were released into the blood from the second-generation schizonts. The second-generation merozoites preferentially invaded into reticulocytes and developed to stage II gametocytes. Enhanced development of stage II gametocytes to mature gametocytes was observed in the reticulocytes in vivo and in vitro in the bleeding group. Nevertheless, invasion of reticulocytes by the second-generation merozoites was not considered to be absolutely necessary for the development of gametocytes.

Cord blood transferrin receptors to assess fetal iron status

OBJECTIVE

To study iron status at different gestational ages using cord blood serum transferrin receptors (STfRs).

METHODS

STfRs, iron, ferritin, total iron binding capacity, haemoglobin, and reticulocytes were measured in 144 cord blood samples. The babies were divided into three groups according to gestation (26 very preterm (24-29 weeks); 50 preterm (30-36 weeks); 68 term (37-41 weeks)).

RESULTS

Serum iron, ferritin, and total iron binding capacity were highest at term, whereas reticulocytes were highest in the very preterm. STfR levels were not influenced by gestation. Haemoglobin (r = 0.46; p < 0.0001) and reticulocytes (r = 0.42; p < 0.0001) were the only indices that independently correlated with STfR levels.

CONCLUSIONS

STfR levels in cord blood are not directly influenced by gestation and probably reflect the iron requirements of the fetus for erythropoiesis.

Reticulocyte subpopulations and reticulocyte maturity index (RMI) rise as body iron status falls

To investigate the influence of body iron status on reticulocyte subpopulations and reticulocyte maturity index (RMI), we measured serum iron markers, fluorescent intensity of reticulocytes, and serum transferrin receptor (sTfR) concentrations in 374 females aged 14-19 years. Reticulocyte subpopulations were analyzed by flow cytometry, and sTfR concentration was measured by enzyme immunoassay. There were no significant differences in the values of reticulocyte subpopulations and RMI between ferritin alone-depleted group and healthy controls. However, middle- and high-fluorescence reticulocytes and RMI were significantly higher in both the serum iron- and serum ferritin-depleted groups than in the ferritin alone-depleted group. Middle-fluorescence reticulocytes and RMI increased gradually as the body iron store was depleted and were 3.4- and 3.6-fold higher, respectively, than normal controls, when the subjects attained a frank iron-deficiency anemia. There were no significant changes in the values of red blood cells or total reticulocyte counts during iron-depleted states. The mean value of sTfR (3.98 mg/l) in the subjects with RMI > or = 1.5% was significantly higher than that (2.26 mg/l) in the subjects with RMI < 1.5% (P < 0.01). The sTfR concentration correlated significantly with RMI (r = 0.61, P < 0.01) and middle-fluorescence reticulocytes (r = 0.59, P < 0.01). In short, body iron depletion induces elevation of immature reticulocyte fractions and RMI.

Cation transport and cell volume changes in maturing rat reticulocytes

During maturation, reticulocytes lose membrane material, including transporters, and this is accompanied by a loss of cell water and volume. Here we determined a possible role of ion transport in adjusting cell volume during maturation. Reticulocytes and red blood cells of different ages were prepared from erythropoietin-treated rats by density gradient fractionation. Cell volume and ion transport were measured in freshly prepared cells and in reticulocytes during in vitro maturation. Reticulocytes had an increased K content and cell volume, whereas intracellular Na was decreased. All parameters approached whole blood values after 2 days in culture. Na-K pump was elevated in reticulocytes and decreased during maturation. Na-K-2Cl cotransport (NKCC) activity was lower in reticulocytes and was activated 8- and 20-fold by shrinkage and okadaic acid, respectively, whereas stimulation was barely detectable in high-buoyant density red blood cells. The ouabain- and bumetanide-insensitive Na flux in reticulocytes decreased on maturation. Most of it was inhibited by amiloride, indicating the presence of Na/proton exchange. Our results show that, although the Na-K-pump activity in reticulocytes is very much increased, the enhanced capacity of NKCC is essentially cryptic until stimulated. Both types of capacities (activities) decrease during maturation, indicating a possible loss of transport protein. The decrease was constrained to the period of reticulocyte maturation. Loss of transport capacity appears to exceed the loss of membrane surface area. Reticulocyte age-related changes in the net electrochemical driving force indicate that the increasing NKCC activity might contribute to the reduction in cell water.

A pharmacodynamic analysis of erythropoietin-stimulated reticulocyte response in phlebotomized sheep

The pharmacodynamics (PD) of the reticulocyte response resulting from phlebotomy-induced erythropoietin (EPO) was investigated in adult sheep. The anemia caused by the controlled phlebotomy (Hb < 4 g/dl, t = 0) resulted in a rapid increase in EPO with peak concentrations from 200 to 1400 mU/ml at 0.5 to 3 days generating a delayed reticulocyte response with peak levels from 9.3 to 14.1% at 2.5 to 5.1 days. The PD EPO-reticulocyte relationship is well described by a simple kinetic model involving 3 relevant physiologic parameters: T(1) = lag-time (0.73 +/- 0.32 days, mean +/- S.D.), T(2) = reticulocyte maturation time (5.61 +/- 1.41 days), and k = EPO efficacy coefficient (0.052 +/- 0.048% g/dl mU/ml/day). Accordingly, 0.52% reticulocytes at 10 g/dl Hb level are generated per day at an EPO concentration of 100 mU/ml. The difference between the T(2) parameter in this study and the maturation time reported for humans may be due to interspecies differences or different technique and experimental conditions. The PD transduction appears largely linear in the observed EPO concentration range, indicating a full utilization of EPO without any significant PD saturation. Also, the EPO concentration versus time profiles resulting from the phlebotomy were similar to exogenous EPO profiles resulting from s.c. therapeutic dosing. This study supports the hypothesis that s.c. EPO dosing is more efficacious than i.v. dosing.

Comparative erythropoietic effects of three vanadium compounds

The biotoxic effects of vanadium are variable depending upon a number of factors including the oxidation state of the test compound. This study reports the effects of three vanadium compounds on peripheral erythrocytes. On day 0 female ICR mice received a single injection of vanadium chloride (V-III), vanadyl sulfate (V-IV), or sodium orthovandate (V-V). At scheduled intervals post-injection, the number of circulating erythrocytes [red blood cells per millimeter cubed (RBC/mm3)], reticulocyte percentages, and radioiron uptake percentages were determined and compared to mice receiving saline only. Data show that all three test substances promoted a significant lowering of RBC/mm3 beginning on day 1 for V-IV and V-V and on day 2 for V-III through day 4. The reticulocyte percentages increase followed the same time course as that of the peripheral RBC decrease. Peak reticulocytosis was noted on days 2 and 4 for all three vanadium-treated groups; for V-IV and V-V the increase continued to day 6. Radioiron data showed an erythropoietic stimulation by a significant increase in uptake percentages on days 4-6 after vanadium injections compared to saline-treated controls.

Different reticulocyte volume in diabetes mellitus patients with and without hypercholesterolemia and/or hypertriglyceridemia

Red cells and reticulocytes from patients with diabetes mellitus (DM) were analysed using laser and computer technology of H*3 hematology analyzer. Four groups of diabetes mellitus patients: diabetes with normolipemia (DM) (n = 12) and DM patients with excess triglyceride (DM-T) (n = 7) or cholesterol (DM-C) (n = 21) or both (DM-TC) (n = 21) were studied. Mean corpuscular volume of mature red cells (Mean +/- SD = 93.6 +/- 5.5 fl) and reticulocyte (119.1 +/- 12.3 fl) of patients with DM-T was not significantly increased from normal (red cell, 90.0 +/- 3.5 fl; reticulocyte, 115.2 +/- 7.3 fl). Plasma triglyceride levels had no significant correlation with red cell MCV, reticulocyte MCV and %Hb A1c. This suggests that high triglyceride levels in DM are not dose-dependent in producing increased MCV of red cells and reticulocytes. Comparing between DM-T and DM-C, red cells and reticulocytes from DM-C patients had significantly decreased MCV (red cell, 85.5 +/- 6.1 fL; reticulocyte, 103.8 +/- 7.4 fL). Plasma cholesterol levels were inversely correlated with MCV of red cells (r = -0.377, p = 0.003) and also MCV of reticulocytes (r = -0.418, p = 0.001). In addition, cholesterol levels showed considerable correlation with Hb A1c (r = 0.572, p = 0.004). The red cell volume change in DM-C patients may be partly due to the shift in balance of cholesterol exchange between red cell membranes and serum lipoproteins.

The cause of the predilection of Babesia gibsoni for reticulocytes

This study was conducted to determine why Babesia gibsoni replicates well in reticulocytes. First, B. gibsoni was cultivated in resealed erythrocyte ghosts loaded with either erythrocyte or reticulocyte lysate, and in reticulocyte ghosts loaded with either erythrocyte or reticulocyte lysate. The parasites multiplied well in the erythrocyte or reticulocyte ghosts loaded with reticulocyte lysate compared to the other resealed cells loaded with erythrocyte lysate. Second, the parasites were cultivated in erythrocytes in culture medium supplemented with either erythrocyte or reticulocyte lysate. The parasites multiplied better in reticulocyte lysate-containing cultures than in erythrocyte lysate-containing cultures. Finally, the parasites were cultivated in erythrocytes in culture medium supplemented with glutamate, aspartate, asparagine, glycine, isoleucine, proline, taurine or GSH, which were present in higher concentrations in reticulocytes than in erythrocytes. Supplementation of the culture medium with glutamate and GSH resulted in enhancement of the multiplication of the parasites, while the other amino acids did not enhance the multiplication. These results indicated that the high levels of the multiplication of B. gibsoni in reticulocytes are partly due to the high concentrations of glutamate and GSH in reticulocytes.

Erythropoietic activity and soluble transferrin receptor level in neonates and maternal blood

Serum transferrin receptor (sTfR) concentration reflects functional iron status and erythropoietic activity. The aims of this study were to examine gender differences of erythropoiesis in newborns and to evaluate the influences of maternal anaemia or iron deficiency on foetal cord blood parameters for iron status and sTfR. In total, 527 newborns and their mothers were examined. Reticulocytes were analysed by flow cytometry and sTfR was measured by an immunoenzymometric method. There were no sex differences in haematological or iron parameters. However, the reticulocyte maturity index (RMI) of male neonates was 37.45%, significantly higher than the 26.81% in female neonates (p <0.01). The high fluorescence reticulocytes (HFR) and middle fluorescence reticulocytes (MFR) of male neonates were 4.91% and 22.36%, respectively, while those of female neonates were 3.31% and 17.83%, respectively (p < 0.01 for each gender). The sTfR concentrations of male and female neonates were 6.27 mg/l and 5.09 mg/l, respectively (p < 0.01). Values for serum iron, ferritin and reticulocyte subpopulations were significantly lower in the newborns of anaemic mothers. However, newborns of iron-deficient mothers showed no differences in iron parameters from those of non-iron-deficient mothers.

CONCLUSIONS

The higher values of RMI and sTfR observed in male neonates indicate that erythropoietic activity is higher in this group. Iron transport to the foetus appears to be independent of maternal iron deficiency. However, iron transport and erythropoiesis in newborns seems to decline from the time that the mothers acquire frank iron deficiency anaemia.

Reticulocyte analysis in iron deficiency anemia and hemolytic anemia

Reticulocyte analysis was studied in 28 anemic patients, 15 with iron deficiency anemia (IDA), and 13 with hemolytic anemia including 9 glucose 6 phosphate dehydrogenase deficiency (G6PD def.), and 4 with G6PD def. combined with HbE trait or alpha thalassemia trait (alpha thal trait). The reticulocyte analysis among these patients showed the increased number of reticulocyte percentage with low degree of maturation in both IDA and G6PD def. patients. The significantly decreased reticulocyte hemoglobin content (CHr) was found in IDA (CHr = 21.74 +/- 4.61 pg in IDA vs 28.41 +/- 1.34 pg in normal; p-value = < 0.0001), whereas, increased CHr was found in G6PD def. patients. In addition, the G6PD def. patients also showed a significant increase in mean corpuscular reticulocyte volume (MCVr) when compared to normal (MCVr = 132.0 +/- 8.39 fl. in G6PD def. vs 110.39 +/- 5.09 in normal; p-value = < 0.0001). However, a significant decrease in MCVr was found in IDA patients (MCVr = 95.89 +/- 8.57 fl.; p-value = < 0.0001 vs normal). From this study, we can suggest that the reticulocyte hemoglobin content (CHr) and mean corpuscular reticulocyte volume (MCVr) are the important defects in patients with iron deficiency anemia.

Human cytogenetic biomonitoring using flow-cytometric analysis of micronuclei in transferrin-positive immature peripheral blood reticulocytes

We have developed a method to isolate and analyze nascent human reticulocytes in peripheral blood for the presence of micronuclei (MN). For a very short time peripheral reticulocytes show residual expression of the transferrin receptor. Using immunomagnetic separation of cells expressing the transferrin receptor, a population of immature reticulocytes (Trf-Ret) was isolated from peripheral blood. In humans, the spleen actively removes micronucleated erythrocytes but during the short lifetime of the isolated Trf-Ret only a fraction (less than about 20%) of the MN-containing reticulocytes will have been eliminated. Cells were stained with the fluorescent dyes Thiazole Orange for RNA and Hoechst 33342 for DNA and analyzed by flow cytometry and fluorescence microscopy. Baseline frequencies of MN-Trf-Ret on a group of healthy donors were found to be 1.1% for males and 1.4% for females; however, the gender difference was not significant. The frequency of MN-Trf-Ret in the studied group increased with age, and was dependent on blood group. In three donors studied over 4 months, the baseline level remained stable. In cancer patients treated with radiation or chemotherapy, the frequency of MN-Trf-Ret increased 10- to 20-fold after 1-4 days, depending on the treatment. A high correlation between flow and manual analysis of MN-Trf-Ret was seen. We believe the method has a high potential as a sensitive and rapid method for biological monitoring in presumed exposed groups and individuals.

Exosomes released during reticulocyte maturation bind to fibronectin via integrin alpha4beta1

Exosomes are vesicles formed in the endosomal compartment and released in the extracellular medium during reticulocyte maturation into erythrocytes. They have a clearing function because of their enrichment with some proteins known to decrease or disappear from the cell surface during maturation, e.g. acetylcholinesterase and transferrin receptor. We show here that integrin alpha4beta1, present on the surface of erythroid precursors but absent from the mature red cell membrane, is at least partly cleared from the reticulocyte plasma membrane by the exosomal pathway. Using flow cytometry, we found that the alpha4 subunit disappears from the reticulocyte surface during in vitro maturation. Two different monoclonal antibodies (B-5G10 and HP 2/1) were used to demonstrate the presence of the alpha4 chain on the exosome surface. Moreover, membrane acetylcholinesterase and lumenal peroxidase-like (i.e. hemoglobin) enzymatic activities were assayed to demonstrate exosome binding to plates coated with increasing fibronectin (FN) concentrations. This interaction was dependent on divalent cations (MnCl2 > MgCl2 > CaCl2). Similarly, vesicles bound to plates coated with the chymotryptic 40 K fragment (FN-40) containing the heparin-binding region of FN. This binding was inhibited by exosome preincubation with fibronectin CS1 peptide and with a monoclonal antibody (HP 2/1) against the integrin alpha4-chain, confirming an alpha4beta1-induced interaction. The importance of the exosome clearance function is highlighted here, since the presence of VLA-4 on reticulocytes often leads to blood circulation complications in some diseases. Moreover, the presence of alpha4beta1 on the exosome surface, by allowing binding to endothelial cells through vascular cell adhesion molecule 1 (VCAM-1), might confer another physiological function to the secreted vesicles.

Kinetic dissection of fundamental processes of eukaryotic translation initiation in vitro

Approaches have been developed for the kinetic dissection of eukaryotic translation initiation in vitro using rabbit reticulocyte ribosomes and a crude preparation of initiation factors. These new approaches have allowed the kinetics of formation of the 43S and 80S ribosomal complexes to be followed and have substantially improved the ability to follow formation of the first peptide bond. The results suggest the existence of a new step on the initiation pathway that appears to require at least one additional factor and the hydrolysis of GTP and may prepare the 80S complex for the formation of the first peptide bond. The initial kinetic framework and methods developed herein will allow the properties of individual species along the initiation pathway to be probed further and will facilitate dissection of the mechanistic roles of individual translation factors and their interplay with RNA structural elements.